For spray-coating with a water-based paint, it is common practice to use a spray booth in order to prevent contamination of the working environment. The booth water is circulated in this spray booth so that the water-based paint which is not deposited on the substrate upon spraying may be trapped by the booth water (referred to as booth circulating water) as an over-spray paint and, therefore, not scattered. However, when the water-based paint finds its way into the booth circulating water, copious surface bubbles are formed and sometimes overflow to contaminate the spray booth and ancillary equipment.
Moreover, while the water-based paint trapped by the booth circulating water is generally recycled, the copious production of bubbles in the booth circulating water and overflows from the spray booth interfere with recovery of the water-based paint, thus causing the problem of a waste of materials. Therefore, in view of better workability and prevention of pollutions, inhibition of bubbling of the booth circulating water has been demanded by the industry.
Japanese Koukai Publication Hei-7-100415 discloses a water-based paint mist elimination device which recovers the bubbles formed on the surface of booth circulating water in one location, taking them out from the spray booth, and destroying the pooled bubbles. Since, in this technology, the bubbles formed in booth circulating water are removed from the spray booth to prevent overflowing, there must be provided a bubble recovery tank and a heater or other device for breaking up the bubbles, so that the equipment is of necessity large-scale.